Cathode active material for lithium secondary battery and lithium secondary battery including the same

ABSTRACT

The cathode active material for a lithium secondary battery according to embodiments of the present invention includes lithium-transition metal composite oxide particles including a plurality of primary particles, and the lithium-transition metal composite oxide particles have a lithium-potassium-containing portion formed between the primary particles. Thereby, it is possible to improve life-span properties and capacity properties by preventing the layer structure deformation of the primary particles and removing residual lithium.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to Korean Patent Application No.10-2021-0030163 filed on Mar. 8, 2021 and Korean Patent Application No.10-2021-0071046 filed on Jun. 1, 2021 in the Korean IntellectualProperty Office (KIPO), the entire disclosure of which is incorporatedby reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a cathode active material for a lithiumsecondary battery and a method of manufacturing the same, and moreparticularly, to a lithium metal oxide-based cathode active material fora lithium secondary battery and a method of manufacturing the same.

2. Description of the Related Art

A secondary battery is a battery which can be repeatedly charged anddischarged. With rapid progress of information and communication, anddisplay industries, the secondary battery has been widely applied tovarious portable telecommunication electronic devices such as acamcorder, a mobile phone, a laptop computer as a power source thereof.Recently, a battery pack including the secondary battery has also beendeveloped and applied to an eco-friendly automobile such as a hybridvehicle as a power source thereof.

Examples of the secondary battery may include a lithium secondarybattery, a nickel-cadmium battery, a nickel-hydrogen battery and thelike. Among them, the lithium secondary battery has a high operatingvoltage and a high energy density per unit weight, and is advantageousin terms of a charging speed and light weight, such that developmentthereof has been proceeded in this regard.

The lithium secondary battery may include: an electrode assemblyincluding a cathode, an anode, and a separation membrane (separator);and an electrolyte in which the electrode assembly is impregnated. Inaddition, the lithium secondary battery may further include, forexample, a pouch-shaped outer case in which the electrode assembly andthe electrolyte are housed.

As an active material for a cathode of a lithium secondary battery, alithium-transition metal composite oxide may be used. Examples of thelithium-transition metal composite oxide may include a nickel-basedlithium metal oxide.

A lithium secondary battery having longer life-span, high capacity, andoperational stability is required as the application range thereof isexpanded. In the lithium-transition metal composite oxide used as theactive material for a cathode, when non-uniformity in the chemicalstructure is caused due to precipitation of lithium, etc., it may bedifficult to implement a lithium secondary battery having desiredcapacity and life-span. In addition, when a deformation or damage of thelithium-transition metal composite oxide structure is caused duringrepeated charging and discharging, life-span stability and capacitymaintenance properties may be reduced.

For example, Korean Patent Registration Publication No. 10-0821523discloses a method of removing lithium salt impurities by washing alithium-transition metal composite oxide with water, but there is alimitation in sufficient removal of the impurities, and a damage to thesurface of particles may be caused in a water washing process.

PRIOR ART DOCUMENT

[Patent Document]

(Patent Document) Korean Patent Registration Publication No. 10-0821523

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cathode activematerial for a lithium secondary battery having improved operationalstability and electrochemical properties, and a method of manufacturingthe same.

Another object of the present invention to provide a lithium secondarybattery including the cathode active material having improvedoperational stability and electrochemical properties.

To achieve the above objects, according to an aspect of the presentinvention, there is provided a cathode active material for a lithiumsecondary battery including: a lithium-transition metal composite oxideparticles comprising a plurality of primary particles, wherein thelithium-transition metal composite oxide particle comprises alithium-potassium-containing portion formed between the primaryparticles.

In some embodiments, the lithium-potassium-containing portion mayinclude a lithium-potassium-sulfur-containing portion which containslithium, potassium and sulfur.

In some embodiments, the primary particles may have a hexagonalclose-packed structure.

In some embodiments, the lithium-transition metal composite oxideparticle may have no primary particle having a face centered cubicstructure.

In some embodiments, a sulfur content of the lithium-transition metalcomposite oxide particle measured through a carbon-sulfur (CS) analyzermay be 1,100 to 4,500 ppm based on a total weight of thelithium-transition metal composite oxide particle.

In some embodiments, a potassium concentration of thelithium-potassium-containing portion measured through energy dispersivespectroscopy (EDS) may be greater than the potassium concentration inthe primary particles measured through the EDS.

In some embodiments, an average potassium signal value of thelithium-potassium-containing portion measured through the EDS may be 1.2to 4 times the average potassium signal value in the primary particlesmeasured through the EDS.

In some embodiments, a content of lithium carbonate (Li₂CO₃) remainingon the surface of the lithium-transition metal composite oxide particlemay be 2,500 ppm or less, and a content of lithium hydroxide (LiOH)remaining on the surface of the lithium-transition metal composite oxideparticle is 2,500 ppm or less.

According to another aspect of the present invention, there is provideda method of manufacturing a cathode active material for a lithiumsecondary battery, including: preparing a preliminary lithium-transitionmetal composite oxide particle; mixing the preliminarylithium-transition metal composite oxide particle with a potassiumcompound aqueous solution; and performing a heat treatment on the mixedpreliminary lithium-transition metal composite oxide particles and thepotassium compound aqueous solution, to prepare lithium-transition metalcomposite oxide particle comprising a plurality of primary particles anda lithium-potassium-containing portion formed between the primaryparticles.

In some embodiments, the potassium compound aqueous solution may beformed by mixing a solvent with potassium compound powder, and an inputamount of the potassium compound powder may be 0.2 to 1.9% by weightbased on a total weight of the preliminary lithium-transition metalcomposite oxide particle.

In some embodiments, an input amount of the solvent may be 2 to 15% byweight based on the total weight of the preliminary lithium-transitionmetal composite oxide particle.

In some embodiments, the potassium compound powder may be potassiumhydrogen sulfate (KHSO₄) powder.

In some embodiments, the heat treatment may be performed at 200 to 400°C. under an oxygen atmosphere.

In some embodiments, the preliminary lithium-transition metal compositeoxide particles may be mixed with the potassium compound aqueoussolution without water washing treatment.

According to another aspect of the present invention, there is provideda lithium secondary battery including: a cathode which comprises acathode active material layer comprising the cathode active material fora lithium secondary battery according to the above-describedembodiments; and an anode disposed to face the cathode.

The cathode active material according to embodiments of the presentinvention may include lithium-transition metal composite oxide particlesincluding the plurality of primary particles, and the lithium-transitionmetal composite oxide particles may include thelithium-potassium-containing portion formed between the primaryparticles. In this case, residual lithium located on the surface of thelithium-transition metal composite oxide reacts with thepotassium-containing compound to be converted into thelithium-potassium-containing portion, such that initial capacity andbattery efficiency properties may be improved.

In some embodiments, by forming the lithium-potassium-containing portionhaving a hexagonal close-packed structure between the primary particlesin the lithium-transition metal composite oxide, the surface of theprimary particles is protected by the lithium-potassium-containingportion, such that the life-span properties and driving stability may beimproved.

In the method of manufacturing a cathode active material according tothe embodiments of the present invention, a potassium compound aqueoussolution may be prepared by mixing a solvent in an amount of 2 to 15 wt.% based on the total weight of the preliminary lithium-transition metalcomposite oxide particles with potassium compound powder in an amount of0.2 to 1.9 wt. % based on the total weight the preliminarylithium-transition metal composite oxide particles without including awater washing treatment process. The potassium compound aqueous solutionmay be mixed with the preliminary lithium-transition metal compositeoxide particles.

In this case, it is possible to prevent the primary particles of thelithium-transition metal composite oxide particles from being deformedfrom the hexagonal close-packed structure to the face centered cubicstructure during water washing treatment. Thereby, it is possible toprevent the initial capacity and life-span properties of the secondarybattery from being reduced. In addition, residual lithium located on thesurface portion of the lithium-transition metal composite oxideparticles and between the primary particles is removed, such that adeterioration in the life-span properties due to gas generation may beprevented, and battery resistance may be reduced to improve initialcapacity.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a process flow chart illustrating a method of manufacturing acathode active material according to exemplary embodiments;

FIGS. 2 and 3 are a schematic plan view and a cross-sectional view of alithium secondary battery according to exemplary embodiments,respectively;

FIGS. 4(a) and 4(b) are high-resolution transmission electron microscopy(HR-TEM) images of lithium-transition metal composite oxide particlesaccording to Example 1;

FIGS. 5(a) and 5(b) are HR-TEM images of lithium-transition metalcomposite oxide particles according to Comparative Example 1;

FIGS. 6(a) and 6(b) are fast Fourier transform (FFT) images in a regionA of FIG. 4(b) and FFT images in a region B of FIG. 5(b); and

FIG. 7 is a graph illustrating potassium signal values of a primaryparticle region and a region between the primary particles (e.g., alithium-potassium-containing portion) of Examples 1 to 5.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a cathode active materialincluding lithium-transition metal composite oxide particles and alithium secondary battery including the same.

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.However, these embodiments are merely an example, and the presentinvention is not limited to the specific embodiments described as theexample.

In exemplary embodiments, the cathode active material may include alithium-transition metal composite oxide particle including a pluralityof primary particles, and the lithium-transition metal composite oxideparticle may include a lithium-potassium (Li—K)-containing portionformed between the primary particles.

In some embodiments, the primary particle may have a single crystal orpolycrystalline structure in crystallography.

For example, the primary particles may include nickel (Ni), and mayfurther include at least one of cobalt (Co) and manganese (Mn).

For example, the primary particles may have a composition represented byFormula 1 below:Li_(a)Ni_(x)M_(1-x)O_(2+y)  [Formula 1]

In Formula 1, a, x and y may be in a range of 0.9≤a≤1.2, 0.5≤x≤0.99, and−0.1≤y≤0.1, respectively. M may represent at least one element selectedfrom Na, Mg, Ca, Y, Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag,Zn, B, Al, Ga, C, Si, Sn, Ba or Zr.

In some preferred embodiments, a molar ratio or concentration x of Ni inFormula 1 may be 0.8 or more.

For example, when employing a composition of high-nickel (high-Ni)contents in which x is 0.8 or more, calcination of thelithium-transition metal composite oxide particles may be performed at arelatively low temperature. In this case, an amount of residual lithiumgenerated on the surface of the lithium-transition metal composite oxideparticles may be increased. Accordingly, a water washing process or anon-water washing process (e.g., an initial wetting method) for removingthe same may be performed. Therefore, when x is 0.8 or more, forexample, the above process for removing the residual lithium may besubstantially significant.

Ni may be provided as a transition metal associated with the output andcapacity of the lithium secondary battery. Therefore, as describedabove, by employing the composition of high-nickel (high-Ni) contents inthe lithium-transition metal composite oxide particles, it is possibleto provide a high-power cathode and a high-power lithium secondarybattery.

However, as the content of Ni is increased, the long-term storagestability and life-span stability of the cathode or the secondarybattery may be relatively deteriorated. However, according to exemplaryembodiments, by including Co, the life-span stability and capacityretention properties may be improved through Mn while maintainingelectrical conductivity.

In some embodiments, the lithium-potassium-containing portion mayinclude a lithium-potassium-sulfur (Li—K—S)-containing portion whichcontains lithium, potassium and sulfur (S). For example, thelithium-potassium-containing portion may include LiKSO₄. In this case,the output properties of the secondary battery may be improved due tothe excellent conductivity of LiKSO₄.

In some embodiments, the primary particles of the lithium-transitionmetal composite oxide particles may have a hexagonal close-packedstructure. Accordingly, a large amount of lithium and transition metalelements may be included in a stable structure having a layered formeven in a small space, such that the capacity properties and life-spanproperties of the secondary battery may be improved.

In some embodiments, a potassium concentration of thelithium-potassium-containing portion measured through energy-dispersiveX-ray spectroscopy (EDS) may be greater than the potassium concentrationin the primary particles measured through the EDS. In this case, thelithium-transition metal composite oxide particles may form aconcentration gradient across the primary particles and thelithium-potassium-containing portion.

For example, an average potassium signal value of thelithium-potassium-containing portions measured through the EDS may be1.2 to 4 times greater than the average potassium signal value in theprimary particles.

When a ratio of the average potassium signal value satisfies the aboverange, the lithium-potassium-containing portion having a hexagonalclose-packed structure may be sufficiently formed between the primaryparticles included in the lithium-transition metal composite oxideparticles. In this case, the surface of the primary particles may beprotected by the lithium-potassium-containing portion, thereby reducingan area where the primary particles are exposed to an electrolyte.Accordingly, the life-span properties of the secondary battery may beimproved. In addition, as residual lithium on the surface of thelithium-transition metal composite oxide particles has been sufficientlyremoved, the electrochemical properties of the secondary battery may beimproved in this state.

In some embodiments, a content of lithium precursor remaining on thesurface of the lithium-transition metal composite oxide particles may becontrolled.

For example, the content of lithium carbonate (Li₂CO₃) remaining on thesurface of the lithium-transition metal composite oxide particles may be2,500 ppm or less, and the content of lithium hydroxide (LiOH) remainingon the surface of the lithium-transition metal composite oxide particlesmay be 2,500 ppm or less.

When the contents of lithium carbonate and lithium hydroxide satisfy theabove ranges, a resistance may be decreased during lithium ion movement,such that the initial capacity properties and output properties of thelithium secondary battery may be improved, and life-span propertiesduring repeated charging and discharging may be enhanced.

In some embodiments, a sulfur content included in the lithium-transitionmetal composite oxide particles may be 1,100 to 4,500 ppm based on atotal weight of the lithium-transition metal composite oxide particles.For example, a lithium-sulfur compound present on the surface of thelithium-transition metal composite oxide particles may not only protectthe surface of the particles from the electrolyte, but alsoadvantageously act on the lithium ion movement in the electrolyte andthe surface. In this case, it is possible to prevent deterioration inthe capacity properties and life-span properties due to excessivepotassium addition, while sufficiently removing residual lithiumtogether with the potassium compound, which will be described below.Accordingly, it is possible to maintain the output properties of thesecondary battery while improving the capacity retention rate thereof.

For example, the sulfur content may be measured through a carbon-sulfur(CS) analyzer.

FIG. 1 is a process flow chart illustrating a method of manufacturing acathode active material according to exemplary embodiments.

Hereinafter, description of the method of manufacturing the cathodeactive material for a lithium secondary battery according to exemplaryembodiments described above will be provided with reference to FIG. 1 .

Referring to FIG. 1 , a preliminary lithium-transition metal compositeoxide particle may be prepared (e.g., step S10).

For example, the preliminary lithium-transition metal composite oxideparticle may be prepared by reacting a transition metal precursor with alithium precursor. The transition metal precursor (e.g., Ni—Co—Mnprecursor) may be prepared through a co-precipitation reaction.

For example, the transition metal precursor may be prepared through aco-precipitation reaction of metal salts. The metal salts may includenickel salts, manganese salts and cobalt salts.

Examples of the nickel salt may include nickel sulfate, nickelhydroxide, nickel nitrate, nickel acetate, and a hydrate thereof, etc.Examples of the manganese salt may include manganese sulfate, manganeseacetate, and a hydrate thereof, etc. Examples of the cobalt salt mayinclude cobalt sulfate, cobalt nitrate, cobalt carbonate, and a hydratethereof, etc.

The metal salts may be mixed with a precipitant and/or a chelating agentin a ratio satisfying the content of each metal or the concentrationratios described with reference to Formula 1 to prepare an aqueoussolution. The aqueous solution may be co-precipitated in a reactor toprepare the transition metal precursor.

The precipitant may include an alkaline compound such as sodiumhydroxide (NaOH), sodium carbonate (Na₂CO₃) and the like. The chelatingagent may include, for example, ammonia water (e.g., NH₃H₂O), ammoniumcarbonate (e.g., NH₃HCO₃) and the like.

The temperature of the co-precipitation reaction may be controlled, forexample, in a range of about 40° C. to 60° C. The reaction time may becontrolled in a range of about 24 to 72 hours.

The lithium precursor compound may include, for example, lithiumcarbonate, lithium nitrate, lithium acetate, lithium oxide, lithiumhydroxide and the like. These compounds may be used alone or incombination of two or more thereof.

In exemplary embodiments, the potassium compound aqueous solution may beinput into the preliminary lithium-transition metal composite oxideparticle and mixed (e.g., step S20).

In some embodiments, the potassium compound aqueous solution may includea solvent and potassium compound powder input into the solvent.

For example, the potassium compound powder may be input in an amount of0.2 to 1.9 wt. % based on the total weight of the preliminarylithium-transition metal composite oxide particle. In this case, it ispossible to prevent deterioration in capacity properties and life-spanproperties due to excessive input of the potassium compound, while theresidual lithium and the potassium compound sufficiently react. Thereby,it is possible to implement a cathode active material having excellentlife-span properties and capacity properties due to having anappropriate sulfur content.

For example, the solvent may be used in an amount of 2 to 15 wt. % basedon the total weight of the preliminary lithium-transition metalcomposite oxide particle. In this case, it is possible to preventdeformation of the layered structure of the primary particles due toexcessive solvent input, while the potassium compound powder is alsosufficiently dissolved. Accordingly, it is possible to maintain thecapacity properties and output properties while improving the life-spanproperties.

In some embodiments, the potassium compound powder may be input into thesolvent so that the content thereof is 50 wt. % or less based on theweight of the solvent to prepare the potassium compound aqueoussolution. When inputting the potassium compound powder into the solventwithin the above range, the potassium compound powder is sufficientlydissolved in the solvent while the residual lithium and the potassiumcompound sufficiently react, such that workability may be improved.

In some embodiments, the potassium compound powder may be potassiumhydrogen sulfate (KHSO₄) powder, and in this case, the potassiumcompound aqueous solution may be a KHSO₄ aqueous solution.

For example, the solvent may be de-ionized water (DIW).

In exemplary embodiments, the preliminary lithium-transition metalcomposite oxide particle and the potassium compound aqueous solution maybe mixed. In this case, potassium and/or sulfur contained in thepotassium compound aqueous solution acts with residual lithium presenton the surface of the preliminary lithium-transition metal compositeoxide particle to be converted into a lithium-potassium-containingportion (e.g., a lithium-potassium-sulfur-containing portion).Accordingly, it is possible to obtain a lithium-transition metalcomposite oxide particle including the primary particles and thelithium-potassium-containing portion. For example, impurities present onthe surface of the preliminary lithium-transition metal composite oxideparticles may be removed through the mixing process. For example, inorder to improve a yield of lithium metal oxide particles or stabilize asynthesis process, the lithium precursor (lithium salt) may be used inan excess amount. In this case, a lithium precursor including lithiumhydroxide (LiOH) and lithium carbonate (Li₂CO₃) may remain on thesurface of the preliminary lithium-transition metal composite oxideparticles.

In addition, for example, as the lithium-transition metal compositeoxide particles contain the composition of higher-Ni contents,calcination may be performed at a lower temperature when manufacturingthe cathode. In this case, a content of residual lithium on the surfaceof the lithium-transition metal composite oxide particles may beincreased.

When the residual lithium is removed by washing with water (waterwashing treatment) in substantially the same amount as the cathodeactive material, the residual lithium may be removed, but oxidation ofthe surface of the preliminary lithium-transition metal composite oxideparticle and side reactions with water may be caused, thereby resultingin a damage or collapse of the layered structure of the primaryparticles. In addition, as the layered structure is deformed into theface centered cubic structure, spinel structure and/or rock saltstructure rather than the hexagonal close-packed structure by water, thelithium-nickel-based oxide may be hydrolyzed to form nickel impuritiessuch as NiO or Ni(OH)₂.

However, according to exemplary embodiments of the present application,since the mixing process (e.g., initial wetting method) is performedusing the potassium compound aqueous solution without water washingtreatment, passivation due to the potassium-containing compound may beimplemented on the surface of the lithium-transition metal compositeoxide particles while the mixing process is performed. For example, thelithium-potassium-containing portion in which lithium and potassium arebonded may be formed between the primary particles having the hexagonalclose-packed structure.

The term “initial wetting method” as used herein may refer to, forexample, a method of inputting 15 wt. % or less of water or thepotassium compound aqueous solution by, for instance, a spray method,based on the total weight of the lithium-transition metal compositeoxide particles without performing water washing treatment of inputtingwater in an amount substantially the same as or similar to the totalweight of the lithium-transition metal composite oxide particles andstirring.

In addition, since water washing treatment is not performed, forexample, the lithium-transition metal composite oxide particle may notinclude the primary particles having the face centered cubic structure.Therefore, the residual lithium may be effectively removed whilepreventing oxidation and damage to the layered structure due to water onthe particle surface.

For example, when directly mixing the potassium compound powder with thelithium-transition metal composite oxide particle instead of thepotassium compound aqueous solution, since the potassium compound powderdoes not have a capillary force, it cannot spread between the primaryparticles, and most of the potassium compound powder may react with theresidual lithium present on the surface of the secondary particles inwhich the primary particles are aggregated. For example, thelithium-potassium-containing portion may be formed in the form of beingcoated on the surface of secondary particles. In this case, the surfaceof the primary particles may not be sufficiently protected whenimpregnating the electrolyte, and the residual lithium may remain on thesurface between the primary particles, thereby causing an increase inthe battery resistance. Accordingly, the capacity and output propertiesof the battery may be reduced.

According to exemplary embodiments of the present application, theinitial wetting method may be performed using the potassium compoundaqueous solution as described above. In this case, the potassiumcompound aqueous solution may permeate between the primary particles bythe capillary force and react with the residual lithium between theprimary particles to form the lithium-potassium-containing portionbetween the primary particles.

In some embodiments, the potassium compound content in the potassiumcompound aqueous solution may be 0.1 to 2 wt. % based on the totalweight of the preliminary lithium-transition metal composite oxideparticle. In this case, while the lithium-potassium-containing portionis also formed to have an appropriate lithium/potassium content at aposition where the residual lithium was present between the surfaceportion of the preliminary lithium-transition metal composite oxideparticle and the primary particles, substantially as in the case ofwater washing treatment, it is possible to prevent a damage or collapseof the layered structure of the primary particles from being caused.

After the mixing process, a cathode active material including theprimary particles and the lithium-potassium-containing portion may beobtained through a heat treatment (calcination) process (e.g., stepS30).

For example, the preliminary lithium-transition metal composite oxideparticle and the lithium-potassium-containing portion on which themixing process has been performed may be subjected to heat treatmentusing a calcination furnace.

Accordingly, it is possible to obtain lithium-transition metal compositeoxide particles in which the lithium-potassium-containing portion isfixed between the primary particles.

For example, the heat treatment may be performed at 200 to 400° C. underan oxygen atmosphere. In this case, the residual lithium on the surfaceof the preliminary lithium-transition metal composite oxide particlesand the potassium compound of the potassium compound aqueous solutionmay be sufficiently bonded to form the lithium-potassium-containingportion.

FIGS. 2 and 3 are a schematic plan view and a cross-sectional view of alithium secondary battery according to exemplary embodiments,respectively.

Hereinafter, description of a lithium secondary battery including acathode including the cathode active material for a lithium secondarybattery described above will be provided with reference to FIGS. 2 and 3.

Referring to FIGS. 2 and 3 , the lithium secondary battery may include acathode 100, an anode 130, and a separation membrane 140 including thecathode active material which includes the above-describedlithium-potassium-containing portion.

The cathode 100 may include a cathode active material layer 110 formedby applying the above-described cathode active material including thelithium-transition metal oxide particles to a cathode current collector105.

For example, a slurry may be prepared by mixing and stirring thepreliminary lithium-transition metal oxide particles mixed with thepotassium compound aqueous solution with a binder, a conductive materialand/or a dispersant in a solvent. The cathode current collector 105 maybe coated with the slurry, followed by compressing and drying to preparethe cathode.

The cathode current collector 105 may include, for example, stainlesssteel, nickel, aluminum, titanium, copper, or an alloy thereof, andpreferably includes aluminum or an aluminum alloy.

The binder may be selected from, for example, an organic binder such asvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP),polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, etc., or an aqueous binder such as styrene-butadienerubber (SBR), and may be used together with a thickener such ascarboxymethyl cellulose (CMC).

For example, a PVDF-based binder may be used as the binder for formingthe cathode. In this case, an amount of the binder for forming thecathode active material layer 110 may be reduced and an amount of thecathode active material may be relatively increased, thereby improvingthe output and capacity of the secondary battery.

The conductive material may be included to facilitate electron movementbetween the active material particles. For example, the conductivematerial may include a carbon-based conductive material such asgraphite, carbon black, graphene, or carbon nanotubes and/or ametal-based conductive material such as tin, tin oxide, titanium oxide,or a perovskite material such as LaSrCoO₃, and LaSrMnO₃.

The anode 130 may include an anode current collector 125 and an anodeactive material layer 120 formed by coating the anode current collector125 with an anode active material.

The anode active material useable in the present invention may includeany material known in the related art, so long as it can intercalate anddeintercalate lithium ions, without particular limitation thereof. Forexample, carbon-based materials such as crystalline carbon, amorphouscarbon, carbon composite, carbon fiber, etc.; a lithium alloy; a siliconcompound or tin may be used. Examples of the amorphous carbon mayinclude hard carbon, cokes, mesocarbon microbead (MCMB), mesophasepitch-based carbon fiber (MPCF) or the like. Examples of the crystallinecarbon may include graphite-based carbon such as natural graphite,artificial graphite, graphite cokes, graphite MCMB, graphite MPCF or thelike. Other elements included in the lithium alloy may include, forexample, aluminum, zinc, bismuth, cadmium, antimony, silicone, lead,tin, gallium, indium or the like.

The anode current collector 125 may include stainless steel, nickel,aluminum, titanium, copper, or an alloy thereof, and preferably includesaluminum or an aluminum alloy.

In some embodiments, a slurry may be prepared by mixing the anode activematerial with an anode forming binder, a conductive material and/or adispersant in a solvent. The anode current collector may be coated withthe slurry, followed by compressing and drying to prepare the anode 130.

As the binder and the conductive material, materials which aresubstantially the same as or similar to the above-described materialsmay be used. In some embodiments, the binder for forming the anode mayinclude, for example, an aqueous binder such as styrene-butadiene rubber(SBR) for consistency with the carbon-based active material, and may beused together with a thickener such as carboxymethyl cellulose (CMC).

The separation membrane 140 may be interposed between the cathode 100and the anode 130. The separation membrane 140 may include a porouspolymer film made of a polyolefin polymer such as ethylene homopolymer,propylene homopolymer, ethylene/butene copolymer, ethylene/hexenecopolymer, ethylene/methacrylate copolymer. The separation membrane 140may include a nonwoven fabric made of glass fiber having a high meltingpoint, polyethylene terephthalate fiber or the like.

According to exemplary embodiments, an electrode cell is defined by thecathode 100, the anode 130, and the separation membrane 140, and aplurality of the electrode cells are stacked to form a jelly roll typeelectrode assembly 150, for example. For example, the electrode assembly150 may be formed by winding, lamination, folding, or the like of theseparation membrane 140.

The electrode assembly may be housed in an outer case 160 together withthe electrolyte, such that a lithium secondary battery may be defined.According to exemplary embodiments, a non-aqueous electrolyte may beused as the electrolyte.

The non-aqueous electrolyte includes a lithium salt as an electrolyteand an organic solvent. The lithium salt is represented by, for example,Li⁺X⁻ and may include F⁻, Cl⁻, Br⁻, I⁻, NO₃ ⁻, N(CN)₂ ⁻, BF₄ ⁻, ClO₄ ⁻,PF₆ ⁻, (CF₃)₂PF₄ ⁻, (CF₃)₃PF₃ ⁻, (CF₃)₄PF₂ ⁻, (CF₃)₅PF⁻, (CF₃)₆P⁻,CF₃SO₃ ⁻, CF₃CF₂SO₃ ⁻, (CF₃SO₂)₂N⁻, (FSO₂)₂N⁻, CF₃CF₂(CF₃)₂CO⁻,(CF₃SO₂)₂CH⁻, (SF₅)₃C⁻, (CF₃SO₂)₃C⁻, CF₃(CF₂)₇SO₃ ⁻, CF₃CO₂ ⁻, CH₃CO₂ ⁻,SCN⁻, (CF₃CF₂SO₂)₂N⁻, and the like as an example.

Examples of the organic solvent may use any one of propylene carbonate(PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethylcarbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate,dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane,diethoxyethane, vinylene carbonate, sulforane, γ-butyrolactone,propylene sulfite, and tetrahydrofurane, or a mixture of two or morethereof. These compounds may be used alone or in combination of two ormore thereof.

As shown in FIG. 3 , electrode tabs (a cathode tab and an anode tab) mayprotrude from the cathode current collector 105 and the anode currentcollector 125, respectively, which belong to each electrode cell, andmay extend to one side of the outer case 160. The electrode tabs may befused together with the one side of the outer case 160 to form electrodeleads (a cathode lead 107 and an anode lead 127) extending or exposed toan outside of the outer case 160.

The lithium secondary battery may be manufactured, for example, in acylindrical shape using a can, a square shape, a pouch type or a coinshape.

According to exemplary embodiments, a lithium secondary battery havingimproved life-span and long-term stability while suppressing a decreasein capacity and average voltage by improving chemical stability of thecathode active material by doping or coating with thepotassium-containing compound may be implemented.

Hereinafter, experimental examples including specific examples andcomparative examples will be described to more concretely understand thepresent invention. However, those skilled in the art will appreciatethat such examples are provided for illustrative purposes and do notlimit subject matters to be protected as disclosed in appended claims.Therefore, it will be apparent to those skilled in the art variousalterations and modifications of the embodiments are possible within thescope and spirit of the present invention and duly included within therange as defined by the appended claims.

Example 1

Preparation of Preliminary Lithium-Transition Metal Composite OxideParticles (S10)

NiSO₄, CoSO₄ and MnSO₄ were mixed in a ratio of 0.88:0.09:0.03,respectively, using distilled water from which internal dissolved oxygenis removed by bubbling with N₂ for 24 hours. The solution was input intoa reactor at 50° C., and a co-precipitation reaction was performed for48 hours using NaOH and NH₃H₂O as a precipitant and a chelating agent toobtain Ni_(0.88)Co_(0.09)Mn_(0.03)(OH)₂ as a transition metal precursor.The obtained precursor was dried at 80° C. for 12 hours, and then againdried at 110° C. for 12 hours.

Lithium hydroxide and the transition metal precursor were added to a dryhigh-speed mixer in a ratio of 1.01:1, and the mixture was uniformlymixed for 5 minutes. The mixture was put into a calcination furnace, andheated to 710 to 750° C. at a heating rate of 2° C./min, then maintainedat 710 to 750° C. for 10 hours. Oxygen was passed continuously at a flowrate of 10 mL/min during heating and maintenance. After completion ofthe calcination, the mixture was naturally cooled to room temperature,followed by grinding and classification to prepare a preliminarylithium-transition metal composite oxide particleLiNi_(0.88)Co_(0.09)Mn_(0.03)O₂.

Preparation and Mixing of Potassium Compound Aqueous Solution (S20), andHeat Treatment (S30)

Potassium hydrogen sulfate (KHSO₄) powder in an amount of 0.8 wt. %based on the total weight of the preliminary lithium-transition metalcomposite oxide particles was input into de-ionized water (DIW) in anamount of 5 wt. % based on the total weight of the obtained preliminarylithium-transition metal composite oxide particles, and then the mixturewas stirred so that the potassium hydrogen sulfate powder wassufficiently dissolved in the de-ionized water to prepare a potassiumcompound aqueous solution.

The prepared potassium compound aqueous solution was input into thepreliminary lithium-transition metal composite oxide particles andmixed.

The mixture was put into the calcination furnace, heated to atemperature between 200 and 400° C. at a heating rate of 2° C./min whilesupplying oxygen at a flow rate of 10 mL/min, and maintained at theheated temperature for 10 hours. After completion of the calcination,the calcined product was classified by 325 mesh to obtain a cathodeactive material.

Manufacture of Lithium Secondary Battery

A secondary battery was manufactured using the above-described cathodeactive material. Specifically, the cathode active material, Denka Blackas a conductive material, and PVDF as a binder were mixed in a massratio composition of 93:5:2, respectively, to prepare a cathode slurry.Then, the slurry was applied to an aluminum current collector, followedby drying and pressing the same to prepare a cathode. After the press, atarget electrode density of the cathode was adjusted to 3.0 g/cc.

Lithium metal was used as an anode active material.

The cathode and anode prepared as described above were notched in acircular shape having a diameter of Φ14 and Φ16, respectively, andlaminated, then an electrode cell was prepared by disposing a separationmembrane (polyethylene, thickness: 13 μm) notched to Φ19 between thecathode and the anode. The prepared electrode cell was put into a coincell outer case having a specification of diameter of 20 mm and a heightof 1.6 mm, then an electrolyte was injected and assembled, followed byaging for 12 hours or more so that the electrolyte could be impregnatedinside the electrodes.

The electrolyte used herein was prepared by dissolving 1M LiPF₆ solutionin a mixed solvent of EC/EMC (30/70; volume ratio).

The secondary battery manufactured as described above was subjected toformation charging-discharging (charge condition: CC-CV 0.1 C 4.3 V0.005 C CUT-OFF, discharge condition: CC 0.1 C 3 V CUT-OFF).

Example 2

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatpotassium hydrogen sulfate (KHSO₄) powder was input in an amount of 0.4wt. % based on the total weight of the preliminary lithium-transitionmetal composite oxide particle.

Example 3

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatpotassium hydrogen sulfate (KHSO₄) powder was input in an amount of 1.6wt. % based on the total weight of the preliminary lithium-transitionmetal composite oxide particle.

Example 4

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatpotassium hydrogen sulfate (KHSO₄) powder was input in an amount of 0.1wt. % based on the total weight of the preliminary lithium-transitionmetal composite oxide particle.

Example 5

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatpotassium hydrogen sulfate (KHSO₄) powder was input in an amount of 2.0wt. % based on the total weight of the preliminary lithium-transitionmetal composite oxide particle.

Comparative Example 1

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1 except that,without performing the step of mixing the preliminary lithium-transitionmetal composite oxide particles with the potassium compound aqueoussolution, the preliminary lithium-transition metal composite oxideparticles were input into 100 wt. % of de-ionized water based on thetotal weight of the preliminary lithium-transition metal composite oxideparticles, and the mixture was subjected to water washing treatment bystirring for 10 minutes, followed by drying at 130 to 170° C. undervacuum for 12 hours after filtering.

Comparative Example 2

A cathode active material and a lithium secondary battery were obtainedaccording to the same procedures as described in Example 1, except thatde-ionized water was input in an amount of 5 wt. % based on the totalweight of the preliminary lithium-transition metal composite oxideparticle instead of the potassium compound aqueous solution and mixed.

The above-described examples and Comparative Example 2 were performed byan initial wetting method in which a small amount of solution or waterwas input, not the water washing treatment in which substantially thesame amount of water as the cathode active material was input, and inComparative Example 1, the water washing treatment was performed.

Experimental Example 1

(1) High-Resolution Transmission Electron Microscopy (HR-TEM) and FastFourier Transform (FFT) Image Analysis

Through HR-TEM analysis and FFT image analysis on cross-sections of thelithium-transition metal composite oxide particles obtained according tothe above-described examples and comparative examples, the structure ofthe compound present in the primary particle region and thelithium-potassium-containing portion (a region between the primaryparticles) was analyzed.

(2) Calculation of Average Potassium Signal Value

The lithium-transition metal composite oxide particles preparedaccording to the above-described examples and comparative examples werecontinuously measured by line scan to obtain potassium signal values ina primary particle region and the region between the primary particles(e.g., lithium-potassium-containing portion) through STEM-EDS.Thereafter, by averaging the potassium signal values for each region, anaverage potassium signal value of the primary particles and thelithium-potassium-containing portion was calculated.

(3) Measurement of Sulfur Content

To measure a content of sulfur (S), a C/S analyzer (carbon/sulfuranalysis equipment; model name: CS844, manufacturer: LECO) was used, andan amount of sample was selected according to the range of measurementvalues of the standard sample measured when drawing up a calibrationcurve.

Specifically, 0.02 to 0.04 g of lithium-transition metal composite oxideparticles obtained according to the above-described examples andcomparative examples were input into the ceramic crucible, and at thistime, a combustion improver (LECOCEL II) and IRON chips were mixed in aratio of 1:1 together.

Thereafter, O₂ was supplied as a combustion gas at 3 L/min in ahigh-frequency induction furnace and burned at about 2,600 to 2,700° C.The sulfur oxide-based inorganic compound gas (e.g., sulfuric acid gas)generated by the combustion is passed through an infrared detectioncell, and a change in infrared absorption compared to the blank wasmeasured to quantitatively detect the sulfur content in thelithium-transition metal composite oxide particles.

Input amounts of potassium hydrogen sulfate powder, input amounts ofsolvent, and the above-described measurement and evaluation results ofthe examples and comparative examples are shown in Table 1 below.

TABLE 1 Average Potassium potassium hydrogen Average signal sulfatepotassium value of (KHSO₄) signal lithium- powder Solvent value ofpotassium- input input primary containing Sulfur Process amount amountparticles portion Signal content Section type (wt. %) (wt. %) (counts)(counts) ratio (ppm) Example 1 Initial 0.8 5 0.231 0.608 2.63 2,400wetting Example 2 Initial 0.4 5 0.155 0.249 1.61 1,580 wetting Example 3Initial 1.6 5 0.154 0.532 3.46 3,100 wetting Example 4 Initial 0.1 50.163 0.194 1.19 1,080 wetting Example 5 Initial 2 5 0.188 0.075 4.104,600 wetting Comparative Water — 100 — — — 630 Example 1 washingtreatment Comparative Initial — 5 — — — 700 Example 2 wetting

FIG. 4 is HR-TEM images of lithium-transition metal composite oxideparticles according to Example 1. Specifically, FIG. 4(a) is an HR-TEMimage of the lithium-transition metal composite oxide particles ofExample 1, and FIG. 4(b) is an enlarged HR-TEM image of a surface region(a region 1) of the primary particles in FIG. 4(a).

FIG. 5 are HR-TEM images of lithium-transition metal composite oxideparticles according to Comparative Example 1. Specifically, FIG. 5(a) isan HR-TEM image of the lithium-transition metal composite oxideparticles of Comparative Example 1, and FIG. 5(b) is an enlarged HR-TEMimage of an inner region (a region 2) of the primary particles in FIG.5(a).

FIG. 6 is FFT images in a region A in FIG. 4 b ) and a region B of FIG.5(b). Specifically, FIG. 6(a) is an enlarged FFT image of region A inFIG. 4(b), and FIG. 6(b) is an enlarged FFT image of area B in FIG.5(b).

Referring to FIGS. 4 to 6 , in the case of Comparative Example 1, sincethe water washing process was performed instead of the initial wettingmethod, even the layered structure in the inner region (e.g., the region2 of FIG. 5(a) and region B in FIG. 5(b)) of the primary particleshaving a relatively low probability of damage to the layered structurewas deformed into a face centered cubic structure from the hexagonalclose-packed structure as shown in 6(b).

On the other hand, in the case of Example 1 in which the mixing process(e.g., initial wetting method) was performed by adding the potassiumcompound aqueous solution, the layered structure in the surface region(e.g., the region 1 of FIG. 4(a) and region A in FIG. 4(b)) of theprimary particles having a relatively high probability of damage to thelayered structure was maintained in the hexagonal close-packed structureas shown in 6(b).

FIG. 7 is a graph illustrating potassium signal values of the primaryparticle region and the region between the primary particles (e.g.,lithium-potassium-containing portion) of Examples 1 to 5.

Referring to FIG. 7 , in Examples 1 to 3, a ratio of the averagepotassium signal value in the region between the primary particles tothe average potassium signal value in the primary particles (potassiumsignal ratio) satisfied a range of 1.2 to 4.

However, Example 4, in which the potassium compound powder input amountwas less than 0.2 wt. % based on the preliminary lithium-transitionmetal composite oxide particles, exhibited a low potassium signal ratioof less than 1.2 times, such that it was difficult to determine thelithium-potassium-containing portion in the lithium-transition metalcomposite oxide particles.

In addition, Example 5, in which the amount of the potassium compoundpowder input was greater than 1.9 wt. % based on the preliminarylithium-transition metal composite oxide particles, exhibited apotassium signal ratio exceeding 4 times.

On the other hand, in the case of Example 1, the signal ratio ofpotassium from the region between the primary particles (e.g.,lithium-potassium-containing portion) to the 50 nm section was uniformlyshown as 2.63 times.

Experimental Example 2

(3) Measurement of Residual Lithium (Li₂CO₃, LiOH) Content

1.5 g of each of the cathode active materials of the examples andcomparative examples was quantified in a 250 mL flask, 100 g ofdeionized water was input then a magnetic bar was put thereto, and themixture was stirred at a speed of 60 rpm for 10 minutes. Thereafter, 100g was sampled after filtering using a flask at reduced pressure. Thesampled solution was put into a container of automatic titrator andautomatically titrated with 0.1N HCl referring to the Wader's method tomeasure Li₂CO₃ and LiOH contents in the solution.

(4) Measurement of Initial Charge/Discharge Capacity and Evaluation ofInitial Capacity Efficiency

After charging (CC-CV 0.1 C 4.3 V 0.005 C CUT-OFF) the lithium secondarybatteries manufactured according to the above-described examples andcomparative examples in a chamber at 25° C., battery capacities (initialcharge capacities) were measured, and after discharging again (CC 0.1 C3.0 V CUT-OFF) the same, the battery capacities (initial dischargecapacities) were measured.

Initial capacity efficiency of each lithium secondary battery wascalculated by dividing the measured initial discharge capacity by themeasured initial charge capacity, then converting it into a percentage(%).

(5) Measurement of Capacity Retention Rate (Life-Time (Cycle)Properties) During Repeated Charging and Discharging

The lithium secondary batteries according to the examples andcomparative examples were repeatedly charged (CC/CV 0.5 C 4.3 V 0.05 CCUT-OFF) and discharged (CC 1.0 C 3.0 V CUT-OFF) 300 times, then thecapacity retention rate was evaluated as a percentage of the dischargecapacity at 300 times divided by the discharge capacity at one time.

The evaluation results are shown in Table 2 below.

TABLE 2 Initial Initial Initial Capacity Content Content chargedischarge capacity retention of Li₂CO₃ of LiOH capacity capacityefficiency rate Section (ppm) (ppm) (mAh/g) (mAh/g) (%) (%) Example 11,670 1,510 239.0 209.9 87.82% 84 Example 2 1,937 1,870 239.5 210.787.97% 79 Example 3 990 1,084 237.3 208.1 87.69% 82 Example 4 2,7002,680 239.7 211.8 88.36% 74 Example 5 1,340 768 236.7 205.9 87.00% 82Comparative 2,210 1,390 237.2 207.8 87.60% 64 Example 1 Comparative3,010 2,730 239.5 212.6 88.80% 68 Example 2

Referring to Table 2, in the case of the examples in which the initialwetting method was performed by mixing the potassium compound aqueoussolution, the content of lithium remaining on the surface of thelithium-transition metal composite oxide particles was reduced comparedto the comparative examples as a whole, and good initial capacityefficiency and excellent life-span properties were secured.

In the case of Example 1 among the examples in which the ratio of theaverage potassium signal values in the primary particles and thelithium-potassium-containing portion satisfied a predetermined range(e.g., 1.2 to 4), the initial capacity was maintained compared toComparative Example 2 in which only the same wt. % of de-ionized waterwas used instead of the potassium compound aqueous solution, as well asimproved life-span properties were secured due to the passivation effectby the lithium-potassium-containing compound formed by reacting withresidual lithium on the surface of the lithium-transition metalcomposite oxide particles.

However, in the case of Example 4 in which the potassium compound powderwas input in an amount of less than 0.2 wt. %, since thepotassium-containing compound to react with the residual lithium was notenough, the residual lithium was slightly increased and the capacityretention rate was slightly reduced compared to Examples 1 to 3.

In addition, in the case of Example 5, in which the potassium compoundpowder was input exceeding 1.9 wt. %, the potassium to react with theresidual lithium was increased to ensure an excellent effect of reducingthe residual lithium, but due to excessive input of the potassiumcompound, discharge capacity, efficiency, and life-span properties wereslightly reduced compared to Examples 1 to 3. In addition, due tounreacted potassium hydrogen sulfate and lithium-potassium-basedcompound on the surface of the active material, the content of residuallithium carbonate (Li₂CO₃) was rather increased compared to Example 3.Further, in the case of Example 5, a trade-off phenomenon, in which thecapacity retention rate was relatively improved due to a decrease in thedischarge capacity, occurred.

In the case of Comparative Example 1 using the conventional waterwashing method, the residual lithium reduction effect was excellent, butas the layered structure of the primary particles is deformed during thewater washing treatment, the initial capacity, efficiency, life-span andelectrochemical properties were greatly reduced compared to the examplesand Comparative Example 2.

DESCRIPTION OF REFERENCE NUMERALS

-   -   100: Cathode    -   105: Cathode current collector    -   107: Cathode lead    -   110: Cathode active material layer    -   120: Anode active material layer    -   125: Anode current collector    -   127: Anode lead    -   130: Anode    -   140: Separation membrane    -   150: Electrode assembly    -   160: Case

What is claimed is:
 1. A cathode active material for a lithium secondarybattery comprising: a lithium-transition metal composite oxide particleincluding a plurality of primary particles, wherein thelithium-transition metal composite oxide particle comprises alithium-potassium-containing portion formed between the primaryparticles, wherein the lithium-potassium-containing portion comprises alithium-potassium-sulfur-containing portion including lithium, potassiumand sulfur.
 2. The cathode active material for a lithium secondarybattery according to claim 1, wherein the primary particles have ahexagonal close-packed structure.
 3. The cathode active material for alithium secondary battery according to claim 2, wherein thelithium-transition metal composite oxide particle has no primaryparticle having a face centered cubic structure.
 4. The cathode activematerial for a lithium secondary battery according to claim 1, wherein asulfur content of the lithium-transition metal composite oxide particlemeasured through a carbon-sulfur (CS) analyzer is 1,100 to 4,500 ppmbased on a total weight of the lithium-transition metal composite oxideparticle.
 5. The cathode active material for a lithium secondary batteryaccording to claim 1, wherein a potassium concentration of thelithium-potassium-containing portion measured through energy dispersivespectroscopy (EDS) is greater than the potassium concentration in theprimary particles measured through the EDS.
 6. The cathode activematerial for a lithium secondary battery according to claim 5, whereinan average potassium signal value of the lithium-potassium-containingportion measured through the EDS is 1.2 to 4 times greater than theaverage potassium signal value in the primary particles measured throughthe EDS.
 7. The cathode active material for a lithium secondary batteryaccording to claim 1, wherein a content of lithium carbonate (Li₂CO₃)remaining on the surface of the lithium-transition metal composite oxideparticle is 2,500 ppm or less, and a content of lithium hydroxide (LiOH)remaining on the surface of the lithium-transition metal composite oxideparticle is 2,500 ppm or less.
 8. A lithium secondary batterycomprising: a cathode comprising a cathode active material layerincluding the cathode active material for a lithium secondary batteryaccording to claim 1; and an anode disposed to face the cathode.
 9. Amethod of manufacturing a cathode active material for a lithiumsecondary battery, comprising: preparing a preliminarylithium-transition metal composite oxide particle; mixing thepreliminary lithium-transition metal composite oxide particle with apotassium compound aqueous solution; and performing a heat treatment onthe mixed preliminary lithium-transition metal composite oxide particleand the potassium compound aqueous solution, to prepare alithium-transition metal composite oxide particle comprising a pluralityof primary particles and a lithium-potassium-containing portion formedbetween the primary particles wherein the potassium compound aqueoussolution is formed by mixing a solvent with potassium compound powder,and an input amount of the potassium compound powder is 0.2 to 1.9% byweight based on a total weight of the preliminary lithium-transitionmetal composite oxide particle, wherein an input amount of the solventis 2 to 15% by weight based on the total weight of the preliminarylithium-transition metal composite oxide particle.
 10. The method ofmanufacturing a cathode active material for a lithium secondary batteryaccording to claim 9, wherein the potassium compound powder is potassiumhydrogen sulfate (KHSO₄) powder.
 11. The method of manufacturing acathode active material for a lithium secondary battery according toclaim 9, wherein the heat treatment is performed at 200 to 400° C. underan oxygen atmosphere.
 12. The method of manufacturing a cathode activematerial for a lithium secondary battery according to claim 9, whereinthe preliminary lithium-transition metal composite oxide particle ismixed with the potassium compound aqueous solution without water washingtreatment.